Circuits for contact meters



Aug. 2, 1960 .1. o. SAINT-AMOUR ETAL 2,947,919

cmcuns FOR CONTACT METERS Filed Feb. 24, 1959 4 Sheets-Sheet l *0 (HO) II J I2 INVENTQRS I JOHN D. SAINTrAMOURG I BYGEORGE .l. CROWDES JR.

ATTORNEY Aug. 2, 1960 J. D SAINT-AMOUR ETAL 2,947,919

cmcuns FOR coumc'r METERS 4 Sheets-Sheet 2 Filed Feb. 24, 1959 I (llO) FIG. 2

I 5 TIME IN MINUTES FIG. 3

INVENTORS JOHN D. SAINT-AMOUR 8 GEORGE 'J. CROWDES JR ATTORNEY g- 1960 J. D. SAINT-AMOUR ETAL 2,947,919

CIRCUITS FOR CONTACT METERS 4 Sheets-Sheet 3 Filed Feb. 24, 1959 INVENTORS JOHN D. .S'A/lVT-AMOUR BY 8 GEORGE J. CROWDES ZF m/zwmg ATTTORA/EX g- 1960 J. D. SAlNT-AMOUR ETAL 2,947,919

CIRCUITS FOR CONTACT METERS Filed Feb. 24, 1959 4 Sheets-Sheet 4 I63 T 37FESA 2/,F.S.A. I64 I- I j v J z g 50-, l/FSA I 5 s g 0 I00 '7 r o- I 50- l 2 3 4 5 TIME m secouos INVENTORS JOHN 0. SAINT- AMOUR 8 BY GEORGE J. CROWDESJF ATTORNEY United States Patent CIRCUITS FOR CONTACT METERS John D. Saint-Amour, Chagrin Falls, and George J.

Crowdes, Jr., Chesterland, Ohio, assignors to Assembly Products, Inc., Chesterland, Ohio, 21 corporation of Ohio Filed Feb. 24, 1959, Ser. No. 795,293

8 Claims. (Cl. 317-152) This application is a continuation-in-part of our copending patent application Serial No. 685,223, filed September 20, 1957.

The present invention relates to electrical control circuits and has particular significance in connection with circuits for galvanometer-type meter relays provided with contacts.

It has long been known to employ electric contact devices of the type having a movable coil rotating within or about a permanent magnet to rotate a pointer thereby operating contacts for making or breaking an electrical circuit when a predetermined coil position is reached. Such a device has the advantage of extreme sensitivity, but has a signal response so delicate it does not of itself develop sufficient torque to make reliable contact for control or indicating purposes. A booster coil, for the purpose of increasing the pressure between the contacts locking them together when they first meet, is helpful, but for some applications uncontrollable according to prior art arrangements. While it has been known to over come some deficiencies by using magnetic attraction between a magnetized stationary contact and pointer contact to insure positive closure of the contacts, such so-called magnetic contacts also have the disadvantage that they cannot be controlled since there is no practical way of varying the magnetization to suit diifering requirements for different times during each operating cycle.

Thus, with most of the' prior art, whether a meter relay is provided with magnetic contacts, or with a booster coil, either arrangement by itself provides no practical way of varying the proportion of attraction to distance per direction in. order to anticipate requirements going up and down. If temperature control in a furnace be taken as an example, there is suflicient thermal lag in the furnace so that as a predetermined control temperature is reached and the furnace is turned off, furnace lining radiations, etc. continue to increase the applied heat, and at times of decreasing temperature, as the temperature is brought to the point where heating current is turned on, continued outward radiation causes cooling below the set point, so that the time-temperature characteristic caused by the controls is one of wide swings, which is not desirable. While it has been known in the past to provide auxiliary heaters and auxiliary thermocouples, with one auxiliary thermocouple arranged to buck and one arranged to boost the main controlling thermocouple to introduce a current component into the thermocouple circuit to offset thermal conditions adverse to stabilization, in other words, to anticipate, such arrangements have the disadvantage of an abundance of associate apparatus and consequent expense of first cost and of maintenance.

It is an object of the present invention to provide simple and inexpensive means for overcoming the abovementioned difliculties.

Another object of the invention is to provide temperature or other control anticipation without the use of auxiliary thermocouples and heaters.

2,947,919 Patented Aug. 2, 1960 Another object of the invention is to provide an improved electrical system of the type adapted to be used both as control and as an indicator, as for industrial load operations, and which is characterized by low cost of construction, ease of maintenance, and more sensitive and accurate control.

While for many applications a solution of the difliculty was found according to the teaching of our above mentioned co-pending application, we have now invented or discovered that it is possible to increase reliability and performance and decrease cost of manufacture and maintenance by eliminating one or more elements claimed as principal components in said application and by making other and related changes and improvements as will hereafter become apparent.

It is accordingly an object of the present invention to provide improved temperature or other control anticipation as shown in Figs. 1 and 2 hereof without the use of the auxiliary condenser shown in Fig. 4 hereof.

Other objects and advantages will become apparent, and the invention may be better understood from consideration of the following description, taken in connection with the accompanying drawing, in which:

Fig. l is a diagrammatical illustration of an improved electrical control and indicating system according to the invention with voltages (for one condition) shown in parentheses.

Fig. 2 is a simplified diagram of a portion of the Fig. l circuit with another condition of steady state volts (in parentheses) Fig. 3 is a graphical representation of temperature vs. time according to prior art compared to according to the invention of this and the aforesaid patent applications.

Fig. 4 is a diagrammatical illustration of a modification; and,

Fig. 5 is a graphical representation of operation of apparatus according to Fig. 4 with different values of resistance and capacitance substituted as hereafter explained.

Broadly speaking, the invention has its basis in our invention or discovery that an increase of voltage upon contact meter contacts, for example, to some point above the usual volts, results, in some sort of electrostatic attraction, even with the use of small contact areas, and that this may be controlled both voltage-wise and in an on-ofl" sense, in a manner which cannot be done by merely shifting the whole response due to either the sensitive coil, or magnetic contacts of conventional nature, or an ordinary'booster coil. Thus arrangements according to the invention may be quite inexpensively made to anticipate, to eliminate false action without causing any error in the signal circuit, and to assure that the contact meter is no longer merely an on-otf device.

Referring now to Fig. 1, lines 10, 11 and 12 may be assumed connected to an A.C. source of 110-220 volt power, to feed the primary of a transformer 13 having secondaries connected to feed a rectifier circuit which in accordance with the illustrated embodiment may comprise full wave rectifiers 14 and 15 and two ZO-mfd. smoothing capacitors 16 and 17, arranged to provide about 300 volts (no load) D.C. between a minus lead 21 and plus lead 22. If desired a mid-tap 23 may also be taken out as to feed a conventional thermocouple break protective resistor (such as that indicated in dash lines at 23R and which may be assumed to be 500,000 ohms).

The A.C. source connections 10 and 11 also power a motor 24 to drive a notched cam 25 having a follower 26 and for repetitively interrupting a circuit through an associate switch 27.

The DC. circuit from connection 22 is taken through switch 27 and then through a 20,000 ohm meter contact current limiting resistor 28, and from there to one side of a coil 29 of a load relay indicated generally at 30. A branch circuit extends from the junction of line 22 and resistor 28 through a 470,000 ohm resistor 31, while in parallel across the series connection of the two resistors 23, 31 is a blocking diode 33.

A contact meter shown diagrammatically generally at 4%? is a moving coil type of meter (which may also serve as an electrical indicator) assumed provided with a permanent magnet (not shown) reactive to which a sensitive coil indicated diagrammatically at 41 turns responsive to changes in a minute quantity of sensitive coil current introduced as from a thermocouple assumed connected to the binding posts marked T.C. If desired, a ten-ohm calibrating resistance 42 may be used in the circuit of the thermocouple leads. Mounted to rotate with coil 41 is a locking coil 43 which provides for one limit of travel an additional, boosting and locking torque as described in various issued patents including 2,576,371 to Thompson and Hammond.

As described in the Thompson and Hammond patent, the coil assembly may be mounted on steel pivots and turn in jewelled bearings with the action restrained by hair-springs, two of which, as indicated diagrammatically at 44 and 45, may also serve to carry current to and from the moving coil assembly. For indicating, a pointer 46 may co-operate with a suitable marked scale plate (not shown) and either a portion of the indicating pointer, or a separate pointer 47, may be used to mate with a relatively stationary contact 48 at a desired limit of travel, to complete a circuit to cause an additional or lockingtorque to aid the sensitive coil torque at the time of contact mating thereby to avoid chattering of the contacts, arcing and circuit interruptions.

In the illustrated embodiment a connection from hair spring 45 through lead 21 serves to complete a circuit from the locking coil (43) back to one side of the load relay coil 29. it will be observed that 21 acts as c ommon' wiring, also completing a circuit from the thermocouple posts T.C. to the sensitive coil 41, also completing a circuit from the locking coil 43 to the negative side of the DC. line, and also completing a circuit from one side of the load relay coil 29 to the negative line from rectifier 15.

The control is shown provided with remote apparatus binding posts 50 (normally-that is with the equipment de-energized-open), E l (common), and 52 (normally closed), while the load relay (shown de-energized) has normally closed contacts -3-4 and 67 and'normally open contacts 4 -5 and 7-8.

Load relay contacts 6--7--8 are respectively associated with the binding posts 50-51-52 as for controlling, and/ or sounding an alarm in connection with, a remote load such as a furnace. For example, see Fig. 2 where a fail-safe arrangement is shown whereby the associate furnace will not heat until the relay 30 (coil 29) pulls in. i

Load relay contacts 3 and 4 are arranged in the circuit of the interrupter motor 24 for eventually interrupting the locking coil current under the influence of the meter contacts 4748. 7

Operation may best be understood by considering just a few elements at a time. As will be seen from Fig. 1 resistance 28 serves to drop the voltage from the 300 volt source as applied toload relay coil 29 down to a voltage, eg. 100 or 110 volts, for which relay coils are usually wound.

If without more this same voltage were carried through tothe meter contacts 47-48 (when open) there would be no particular electrostatic attraction of the one for the other. a I 7 However, in accordance with the present invention, a resistance value (31) is arranged to provide a higher voltage between the contacts (when they are open) whena rectifier (33) is provided to prevent this voltage from bleeding on through the relay coil 29. and/ or resister 28. Thus, because of the presence of rectifier 33, when the meter contacts 47-48 are open, so that there is no current through them (or resistance 31), a full 300 volt difference is presented at the meter contacts (see Fig. 1 voltage values in parentheses).

When the meter contacts are closed, as shown in Fig. 2 (which is a simplified and schematic diagram of a portion of the Fig. 1 circuit, but with the contact-meterclosed condition of assumed steady state voltages shown in parentheses), both contacts assume the voltage across the iocldng coil 43. The equipment easily designed so that this is a 1.6 volt drop, and ultimately the relay coil 29 will have this same voltage and be, in effect, shorted out by the meter contact and locking coil circuit.

This feature of load relay coil shorting by locking coil of i contact circuit is not new per se but it reaches its full fruition of versatility and provides particularly desirable means for assuring electrostatic attraction when used in a combination according to the present invention.

An important feature of the invention is that by merely increasing the voltage on the contacts 47-48 (when open) 7 from a prior art of 70 to 110 volts to about 300 volts,

or even much less, there is caused an electrostatic attraction between the contacts which will serve to anticipate requirements both on the upswing and on the downswing as may be more clear from consideration of Fig. 3, which is a graphical representation of temperature plotted against time, and 1000 is assumed as a desired operating temperature, and where solid curve 70 represents operation with prior art control. With the arrangement of the invention the furnace may be turned ed at some advance point y, and then, with the meter contacts closed (heating contacts open) the furnace may coast through the set point, and at 1, again anticipating, the meter contacts will open before too cool a temperature has been reached. This is so because, although the heating elements are Off from y to z, the contacts 47-43 are closed so that there is no voltage between them and when the locking circuit is periodically interrupted the controlling thermocouple can operate the meter for break-away at a point sooner than would be the case of suflicient voltage for electrostatic attraction never had been applied. This is so because since the sensitive coil did not require so much current (i.e., heat) to operate to closure in the first place, the current (hence heat) will not have to back down so much to permit of contact opening. The end result is that the entire operational curve will be levelled out as indicated by the dashed curve 71, and an advantage of the arrangement of the invention is that needle swing may be greatly reduced, actually from as much as forty percent to less than one percent and thus to a much greater extent than shown by any literal scaling of the curves of Fig. 3.

When the meter contacts are open, as soon as the OE-On switch 61 is turned to On the interrupter motor 24will start but it will continue to break its own circuit under the influence of the energization of load relay 29 and consequent opening of relay contacts 3-4. When the meter contacts 47-48 close (see Fig. 2) relay coil 29 is effectively shorted out and the meter locking current interrupter motor 24 runs continuously but the load relay will not pull in until meter sensitive coil current is such as to allow meter contacts to re-open. With the proportioning voltage application of the invention, no current then circulates through resistance 31 and motor 24 runs cam 25 until follower 26 drops into the first notch, re-energizing relay coil 29. If then the meter contact spacing is such that the contacts are inside the proportioning band, sufficient attraction occurs so that the meter contacts close in a matter of a few seconds. In effect then, taking furnace heat-up as an example, the control of the invention simulates a burst of heat but does it in a period which would not even suffice for heat to reach thermocouple.

We have invented or discovered that this action (which produces a proportioning action on the contacts) is exponential (for example as regards contact closing velocity vs. time) in any event, so that it is not necessary to further complicate the circuit as with networks or an exponential charging condenser such as that shown in Fig. 4 where like parts are like numbered as before but a twowire power circuit is shown, the rectifiers 114, 115 are single (half wave) rectifiers and a current limiting resistor 118 is used in the power circuit. In Fig. 4 the meter contact current limiting resistor 128 may be assumed to have a value of 9500 ohms, and from it a branch circuit extends through a 2 mfd. capacitor '130 and then through a 1000 ohm resistor 131, while a parallel circuit extends from 128 through the diode 33. From the junction of line 22 and resistance 128 a tuning circuit extends through a 100,000 ohm protective resistor 134 and a 1 megohm potentiometer 135 to a point between capacitor 130 and resistor 131, and leads are taken out to test jacks as shown at 153 and 154.

In operation with the arrangement of Fig. 4, when the contact 27 is closed and the load coil relay is energized across the 300 volt line (in series with resistor 128) the condenser 130 is allowed to charge (through resistors 134 and 135) and, if the meter contacts are open, the voltage also builds up on the meter contacts. Rectifier 33 prevents the condenser from discharging until the meter contacts close. When they close, condenser 30 discharges through resistor 31 and through the main meter contacts and locking coil 43 back to wire 21.

i In Fig. 5, the shaded area indicated generally at 160 represents a zone of indeterminate or zero anticipation as is according to the prior art where there is a'relatively low voltage on contact meter contacts. With the arrangement of the invention, however, voltage is furnished higher at proper times, and, depending upon RC constants of the circuit, at a fraction of a second (after closing of 27) suflicient voltage is built up for what might be called 1% of full scale anticipation, shortly thereafter 2% of full scale anticipation is reached, and in a short time thereafter 3% of full scale anticipation is reached.

It is possible to select values of resistance and capacitance (Fig. 4), or with the arrangement of Figs. 1 or 2 it is possible to merely select values of resistance, such that the open circuit voltage between contacts 47 and 48 on the contact meter rather rapidly approach the voltage corresponding to a desired percent of full scale anticipation. In Fig. 5, the curves 161, 162, 163, represent, by way of example, certain voltage-time characteristics dependent on values of R (dependent on setting of 135 of Fig. 4) and selection of C (130 of Fig. 4).

If desired, the main protective resistor 128 (or 28) may be made adjustable, and/or the protective resistor such as 134 may be made adjustable, and a variable capacitor (such as 130) may be provided to make a further adjustment, and the adjustment of any of them may be used to change the time response of the network.

If desired the power supply can be readly arranged to produce any desired voltage and this voltage may, of course, be refined (to control the width of the proportional band of operation) by a potentiometer (such as that indicated dashed at 60 in Fig. 2) feeding the resistance 31 and hence feeding the same voltage to the meter-relay contacts when open. All that remains to be done is to break the contact meter locking circuit at intervals, and this may be achieved in many conventional ways, the motor driven cam switch 24-47 being shown in the illustrated embodiment.

There is thus provided arrangements of the class described capable of meeting the objects above set forth. The new way of anticipating is less expensive and more accurate than anticipating by using auxiliary thermocouples, and the new manner of causing contact closing is less expensive and more controllable than magnetic con- 6 tacts. The arrangement of the invention eliminates false action, causes no errors in signal circuit, and insures that the contact meter is a proportioning device and no longer simply an on-oif device.

While we have illustrated and described a particular embodiment and applied our considerations to temperature control, the arrangements are equally operable for other control and various modifications may obviously be made without departing from the true spirit and scope of the invention which we intend to have defined only by the appended claims and all reasonable equivalents.

We claim:

1. In an electrical control system, a direct current source of a predetermined first voltage, a load relay having a coil rated at less than said first voltage D.C., connections from the source to the relay coil and including a first resistance for dropping the voltage as applied to the coil, a galvanometer type meter having contacts operable from open to closed positions, additional connections including a second resistance having one end connected adjacent the source side of the first resistance so that the second resistance will be substantially unaffected by IR drop in the first resistance and with said additional connections extending from the source through said second resistance to the meter contacts to apply thereto the full voltage of the source when the contacts are open.

2. An anticipatory control system comprising a direct current source of voltage of more than volts, a load relay having a coil designed for normal operation at not more than 125 volts D.C., a meter relay having contacts operable from open to closed positions, a first resistance and connections from said source through said first resistance to the load relay coil and therefrom back to the source, a second resistance and connections from said source through said second resistance to one of the meter contacts and from the other of the meter contacts back to said source to provide an electrostatic attraction between the contacts when opened, a rectifier interposed between the ends remote-from-the-source of the first and second resistances to permit current to flow from the end-remotefrom-the-source of the first to the end-remote-from-thesource of the second, but not from the second to the first, whereby the meter contacts are adapted to short out the load relay coil when said meter contacts are closed without interfering with voltage requisite for providing substantial electrostatic attraction of the meter contacts for each other when opened.

3. An anticipatory control system as in claim 2, further characterized by an adjustable voltage take-off means interposed between source and second resistance and for controlling the width of the proportional band of operation of said anticipatory control system.

4. An anticipatory control system as in claim 2, further characterized by a condenser connected substantially in parallel with the rectifier to delay the build-up of voltage on the meter contacts when open.

5. An anticipatory control system as in claim 2, further characterized by a condenser arranged substantially in parallel with the rectifier, at least a portion of the second resistance being made adjustable, and a third resistance arranged in series with the second resistance adjustable portion and in series with the condenser to provide advantageous time constants which are manually adjustable.

6. An amplifier circuit comprising a contact making galvanometer having a relatively stationary contact and a rotatable position part carrying a sensitive coil and additionally carrying a locking coil and carrying contact means electrically connected in series with said locking coil; said relatively stationary contact co-operating with said rotatable carried contact means to establish an electrical circuit for one limit of travel of the rotatable carried contact means; a source of power of more than 125 volts; a clock motor driven cam contact with the cam contact electrically arranged in series with one side of said source for period- 7 ically breaking a circuit with respect thereto; a first resistance electrically connected in series with said cam contact and source; a second resistance'electrically connected in series with the cam contact and source but substantially independent of the first resistance so that each will only have its own 1R drop and be unafiected by that of the other; a load relay coil connected across the circuit formed by source, cam contact and first resistance; at least one connection establishing a circuit from the end of the second resistance remote -from cam switch and source to the relatively stationary contact; at least one connection connecting the side of the locking coil remote from the rotatable carried contact means to the other side of the source; and a rectifier connected between the circuit from first resistance to relay coil on the one hand and the circuit between second resistance and relatively stationary contact on the other hand and in such current blocking direction sense as to permit locking coil and meter contacts to short out the relay coil when the meter contacts are closed whiie providing an electrostatic charge of more than 125 volts upon the meter contacts when open to provide contact condition anticipation both for closing and for opening (direction) of the meter contacts under control of the sensitive coil of the meter With periodic interruption of the circuits by the opening of the motor driven cam contact depending on energization of the clock motor.

7. An amplifier circuit as in claim 6 further characterized by a pair of load relay contacts normally closed when the load relay is de-energized and open when it is energized, and connections for energizing the clock motor through said relay contacts whereby to cause operation of the clock motor substantially only when the load relay is dropped out and hence when the galvanometer contacts are closed, and means for causing the cam contact to close unless the clock motor is energized, whereby to permit the electrostatic charge to be substantially always available so long as the galvanometer contacts are open.

8. An amplifier circuit comprising a contact making galvanometer having a relatively stationary contact and a rotatable position part carrying a sensitive coil and additionally carrying a locking coi and carrying contact means electrically connected in series with said locking coil; said galvanometer stationary contact cooperating with said rotatable carried contact means to establish an electrical circuit for one limit of travel of the rotatable carried contact means; a source of power; a clock-motor driven cam contact with the cam contact electrically ar'ranged'in series with one side of said source for periodically establishing and breaking a circuit with respect thereto; a first resistance electrically connected in series with said cam contact and source; a second resistance electrically connected in series with the cam contact and source while substantially independent of the first resistance so that each will have only its own IR drop and be unafiected by that of the other; a load relay coil connected across the circuit formed by source; cam contact and first resistance; at least one connection establishing'a circuit from the end of the second resistance remote from cam switch and source to the relatively stationary'limit contact; at least one connection connecting the sideof the locking coil remote from the rotatable carried contact means to the other side of the source; a condenser connected between the circuit from first resistance and relay coil on the one hand and between the second resistance and stationary limit contact on the other hand so as to be charged when the cam contact is closed according to the difference in IR drop in the first with respect to that in the second resistance; and a rectifier connected substantially across the condenser to permit locking coil and meter contacts to short out the relay coil when the meter contacts are closed while providing an electro-static charge of more than volts upon the meter contacts when open to provide contact anticipation bothfor closing and opening of the meter contacts under control of the sensitive coil meter.

References Cited in the file of this patent FOREIGN PATENTS 290,562' Great Britain Oct. 25, 1928 

